The chemistry and physics of cobalt-oxide nanoparticles

Why metal oxides?

Metal oxide nanoparticles are genuinely of great technological relevance because of their wide applications in catalysis, photonics and drug delivery systems. In everyday life, gas sensors allow the detection of environmental molecules based on the metal-oxide-semiconductor-ﬁeld-eﬀect transistor (MOSFET). In such devices small modulations of the conductance of the surface layer critically modify the electric potential across the device. It is then easy to envision that the performance, durability and chemical sensitivity of such a device depends strongly on the crystallographic, electronic and ultimately chemical nature of the oxide surface layer.

Cobalt and cobalt oxide nanoparticles

The interested on cobalt-based nanoparticles reside on both its catalytic and magnetic properties. In magnetism, it is known that the interplay between cobalt low crystallographic anisotropy, size and shape effects can greatly alter their magnetic response. In such nanoparticles, the fine tailoring of the “bulk” and surface anisotropy may result on the desired macroscopic magnetic response. Moreover, control over particles dimensions; crystallographic phase and chemical composition are of great importance in order to understand their functional physical and chemical properties since chemical reactivity depends on them size and defect density.

Methodology: Growth and Characterization

We use buffer-layer assisted growth, where metallic cobalt is evaporated in a oxygen atmosphere and deposit on a substrate covered by a pre-condensed gas layer (buffer-layer). After heating up the substrate to room temperature and degassing the buffer layer we obtain the nanoparticles deposited at very low energies on a solid substrate. The soft-landing achieved by this growth method allows the investigation of the resulting sample by means of surface sensitive techniques such as electron spectroscopies (AES and XPS) and particularly, scanning probe microscopy (AFM and MFM). Also electron microscopies are well-suitable as characterization tools for size distribution, morphology and structural determination. In such studies it crucial determine the particles shape, size and particularly the top-most crystallographic structure.